Uninterruptible Power Supply Systems and Methods for Communications Systems

ABSTRACT

An uninterruptible power supply for supply electrical power to a load, comprises a connection to a primary source for supplying primary power, a battery system for storing battery power, an inverter, and a controller. The controller controls the inverter to operate in a first mode, a second mode, and in a third mode. In the first mode, power is supplied to the primary load and the battery system based on primary power. In the second mode, power is supplied to the primary load based on battery power. In the third mode, power is supplied to the primary source based on battery power.

RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 61/394,300, filed Oct. 18, 2010.

The contents of the application(s) listed above are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to uninterruptible power supplies for usein communications systems and, more specifically, to uninterruptiblepower supplies having sporadically used energy production and/or storagesystems.

BACKGROUND

UPS systems are often designed to be used to provide power to a largercommunications system based on an AC utility power signal generated byan electric utility. Examples of communications systems that might usesuch UPS systems are cable TV (CAN) systems, telephony systems, andcellular telephone systems. Typically, a large number of the UPS systemswill be distributed throughout the communications system.

In a typical UPS system designed to provide power to a primary load, thebattery array is used only when the utility power signal is not presentor out of predetermined parameters, and the battery array may be unusedfor out of predetermined parameters, and the battery array may be unusedfor long periods of time. The battery arrays distributed throughout atypical large communications system are a relatively expensive asset ofsuch communications systems.

The need exists for improved UPS systems and methods that make betteruse of the existing assets forming a communications system.

SUMMARY

The present invention may be embodied as an uninterruptible power supplyfor supply electrical power to a load comprising a connection to aprimary source for supplying primary power, a battery system for storingbattery power, an inverter, and a controller. The controller controlsthe inverter to operate in a first mode, a second mode, and in a thirdmode. In the first mode, power is supplied to the primary load and thebattery system based on primary power. In the second mode, power issupplied to the primary load based on battery power. In the third mode,power is supplied to the primary source based on battery power.

The present invention may also be embodied as a method of supplyingelectrical power to a load comprising the following steps. A batterysystem for storing battery power and an inverter are provided. Theinverter is controlled to operate in a first mode, a second mode, and athird mode. In the first mode, power is supplied to the primary load andthe battery system based on primary power obtained from a primary powersource. In the second mode, power is supplied to the primary load basedon battery power. In the third mode, power is supplied to the primarysource based on battery power.

The present invention may also be embodied as an uninterruptible powersupply for supply electrical power to a load, comprising a connection toa primary source for supplying primary power, a battery system forstoring battery power, an inverter, a transformer, and a controller. Thetransformer is operatively connected between the primary source, thebattery system, and the load. The controller controls the inverter,based on at least one characteristic of the primary power, to operate ina first mode, a second mode, and in a third mode. In the first mode,power is supplied to the primary load and the battery system based onprimary power. In the second mode, power is supplied to the primary loadbased on battery power. In the third mode, power is supplied to theprimary source based on battery power.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first example uninterruptible powersupply (UPS) of the present invention;

FIG. 2 is a flow chart illustrating a first example of control logic forcontrolling the operation of the first example UPS to perform peakshaving;

FIG. 3 is a flow chart illustrating a second example of control logicfor controlling the operation of the first example UPS to perform peakshaving;

FIG. 4 is a flow chart illustrating a third example of control logic forcontrolling the operation of the first example UPS to perform peakshaving;

FIG. 5 is a block diagram of a second example uninterruptible powersupply (UPS) of the present invention;

FIG. 6 is a flow chart illustrating one example of control logic forcontrolling the operation of the second example UPS to perform peakshaving;

FIG. 7 is a block diagram of a third example uninterruptible powersupply (UPS) of the present invention.

DETAILED DESCRIPTION

Referring initially to FIG. 1 of the drawing, depicted therein is afirst example UPS system 20 constructed in accordance with, andembodying, the principles of the present invention. The example UPSsystem 20 is adapted to obtain power from and supply power to a utility22 and also to provide power to a primary load 24. As depicted in FIG.1, a meter 26 may be connected between the utility 22 and the firstexample UPS system 20.

The first example UPS system 20 is designed to be used to provide powerto a larger communications system (partly represented in FIG. 1 by theprimary load) based on an AC utility power signal generated by anelectric utility. Examples of communications systems that might use theUPS system 20 are cable TV (CATV) systems, telephony systems, andcellular telephone systems.

Typically, a large number of the UPS systems such as the example UPSsystem 20 will be distributed throughout the communications system. Ingeneral, a plurality (two or more) and typically tens or hundreds of thefirst example UPS systems will be located where utility power isavailable and distributed throughout the communications system asnecessary to provide an appropriate power signal to components of thecommunications system. Only the example UPS system 20 is depicted inFIG. 1 for purposes of clarity.

Typically, but not necessarily, the utility 22 operates at a standardvoltage (V₁), while the primary load 24 operates at a different voltagelevel (V₂) than the utility 22. When the voltages V₁ and V₂ aredifferent, the transformer 30 thus steps the voltage up or down asnecessary to perform the functions described below. In addition, theprimary load 24 may operate in some environments (e.g., CATV systems)based on an AC power signal and in other environments (e.g., telephonysystems) based on a DC power signal. As is conventional, the batteryarray 34 is one or more batteries that employ a DC power signal. Whilebatteries currently represent the most conventional manner of storingpower for the generation of electricity, other power storage systems maybe used as will be generally discussed in further detail below.

The first example UPS system 20 comprises transformer 30, an invertercircuit 32, a battery array 34, a controller 36, and a servicedisconnect 38. The service disconnect 38 may be operated to disconnectthe transformer from the utility 22. The transformer 30 comprises a core40, a first winding 42, a second winding 44, and a third winding 46.

The first example UPS system 20 may be configured to operate in one ormore of at least three operating modes. In a first (primary) operatingmode, the UPS system 20 supplies power to the primary load 24 andcharges the battery array 34 using power from the utility 22. In asecond (standby) operating mode, the UPS system 20 supplies power to theprimary load 24 using power stored in the battery array 34. In a thirdoperating (peak shaving) mode, the UPS system 20 supplies power to theutility 22 using power stored in the battery array 34. In the firstexample UPS system 20, the controller 36 determines whether the UPSsystem operates in the first, second, or third modes.

In a typical UPS system designed to provide power to a primary load, thebattery array is used only when the utility power signal is not presentor out of predetermined parameters, and the battery array may be unusedfor long periods of time. The provision of the third operating modeallows the operator of the first example UPS system to optimize the useof assets (e.g., batteries) that otherwise typically are unused for longperiods of time. In particular, the operator of the first example UPSsystem 20 can charge the battery array 34 using utility power duringoff-peak utility hours when power prices are relatively cheap and,during peak utility hours when power prices are relatively expensive,sell power back to the utility by discharging the battery array 34. Theoperator of the communications system incorporating the first exampleUPS system 20 may thus profit on the difference between peak and offpeak prices for electrical power.

In a typical UPS system designed to provide power to a primary load, thebattery array is comprised of batteries optimized for continuouscharging and infrequent discharging. While such batteries may be used inthe first example UPS system 20, the example battery array 34 of thefirst example UPS system 20 is preferably comprised of deep cyclebatteries optimized for frequent charging and discharging. The use ofdeep cycle batteries in the example battery array 34 allows the firstexample UPS system to operate in the third operating mode on a frequent(e.g., daily) basis without seriously adversely affecting the life ofthe batteries forming the battery array 34.

However, even deep cycle batteries may be charged and discharged alimited number of times before replacement is required, so the chargingand discharging of the battery array 34 represents a cost to theoperator of the first example UPS system 20. Additionally, the costs ofreplacing particular batteries (e.g., remote or difficult to access) maybe factored into the cost of operating particular battery arrays 34 inthe communications system. Accordingly, the cost to the operator of thecommunications system operating the first example UPS system 20 in termsof reduced battery life may be considered when the controller 36 placesthe UPS system 20 in the third operating mode. In particular, thecontroller 36 may be programmed to place the UPS system in the thirdoperating mode only if the difference between the peak and off-peakelectricity prices is sufficiently high to justify incrementallyreducing the life of the batteries forming the example battery array 34.

Referring now to FIG. 2 of the drawing, depicted therein is a firstexample method 120 that may be implemented by the controller 36 of thefirst example UPS system 20. The first example method 120 begins at ainitial step 130 and initially proceeds to a step 132 which determineswhether the utility power signal generated by the utility 22 is withincertain predetermined conditions (i.e., acceptable). If not, the method120 places the UPS system 20 in the second operating mode at step 134and returns to the initial step 130.

If the utility power signal generated by the utility 22 is within thepredetermined conditions, the method 120 moves to step 140, whichdetermines whether the utility 22 is supplying power at peak or non-peakrates. If the utility 22 is supplying power at non-peak rates, themethod 120 places the system 20 in the first operating mode at step 142and then returns to the initial step 130. If the utility 22 is supplyingpower at peak rates, the method 120 places the system 20 in the thirdoperating mode at step 144 and then returns to the initial step 130.

The first example method 120 thus places primary emphasis on causing theUPS system 20 to provide standby power to the primary load 24 in thesecond operating mode when the utility power signal is unacceptable butcauses the UPS system 20 to operate in either the first operating mode(e.g., charging batteries with relatively cheap power) during non-peaktime periods or in the third operating mode (e.g., selling power back tothe utility) during peak time periods.

Referring now to FIG. 3 of the drawing, depicted therein is a secondexample method 150 that may be implemented by the controller 36 of thefirst example UPS system 20. The second example method 150 begins at ainitial step 160 and initially proceeds to a step 162 which determineswhether the utility power signal generated by the utility 22 is withincertain predetermined conditions (i.e., acceptable). If not, the method150 places the UPS system 20 in the second operating mode at step 164and returns to the initial step 160.

If the utility power signal generated by the utility 22 is within thepredetermined conditions, the method 150 moves to step 170, whichdetermines whether the utility 22 is supplying power at peak or non-peakrates. If the utility 22 is supplying power at non-peak rates, themethod 150 places the system 20 in the first operating mode at step 172and then returns to the initial step 160.

If the utility 22 is supplying power at peak rates, the second examplemethod 150 proceeds to a step 174 at which it is determined whether theexample battery array 34 is within predetermined parameters. As oneexample, the charge on the battery array 34 may be too low to provideadequate standby power to the primary load 24 should the utility powersignal should become unacceptable. As other examples, the age of thebattery array 34 or operating conditions (temperature, humidity, etc.)may be inappropriate for using the battery array 34 for any purposeother than providing standby power to the primary load 22. In any ofthese situations, the method 150 returns to the initial step 160 anddoes not place the example UPS system 20 into the third operating mode.

If, on the other hand, the example battery array 34 is within thepredetermined parameters, the method 150 places the system 20 in thethird operating mode at step 176 and then returns to the initial step160.

The second example method 150 thus places even more emphasis on causingthe UPS system 20 to provide standby power to the primary load 24 bypreventing the UPS system 20 from operating in the third operating modeif the battery array 34 is outside of certain predetermined parameters.Only when the condition of the battery array 34 is appropriate for usein peak shaving will the method 150 place the UPS system 20 in the thirdoperating mode. Otherwise, the second example method 150 causes the UPSsystem 20 to operate in either the first operating mode (e.g., chargingbatteries with relatively cheap power) during non-peak time periods orin the third operating mode (e.g., selling power back to the utility)during peak time periods.

Referring now to FIG. 4 of the drawing, depicted therein is a thirdexample method 220 that may be implemented by the controller 36 of thefirst example UPS system 20. The third example method 220 begins at ainitial step 230 and initially proceeds to a step 232 which determineswhether the utility power signal generated by the utility 22 is withincertain predetermined conditions (i.e., acceptable). If not, the method220 places the UPS system 20 in the second operating mode at step 234and returns to the initial step 230.

If the utility power signal generated by the utility 22 is within thepredetermined conditions, the method 220 moves to step 240, whichdetermines whether the utility 22 is supplying power at peak or non-peakrates. If the utility 22 is supplying power at non-peak rates, themethod 220 places the system 20 in the first operating mode at step 242and then returns to the initial step 230.

If the utility 22 is supplying power at peak rates, the second examplemethod 150 proceeds to a step 244 at which it is determined whether aprofit margin, or difference between peak and non-peak rates, issufficient to justify the discharge/charge cycle required to sell powerback to the utility 22. As generally discussed above, each charge anddischarge cycle reduces the overall life of the batteries forming thebattery array 34. This reduction in overall life of the battery arraycan be quantified and compared with the possible revenue derived fromselling energy back to the utility 22. If step 174 determines that thismargin is too low to justify the reduction in battery life, the method220 returns to the initial step 230 and does not place the example UPSsystem 20 into the third operating mode.

If, on the other hand, the margin is within predetermined parameters(e.g., above a minimum), the method 220 places the system 20 in thethird operating mode at step 246 and then returns to the initial step230.

The third example method 220 thus takes into account additionalvariables when determining whether selling power back to the utility 22is justified. Only when the profit margin exceeds the cost associatedwith charging and discharging the battery will the method 220 place theUPS system 20 in the third operating mode. Otherwise, the second examplemethod 150 causes the UPS system 20 to operate in either the firstoperating mode (e.g., charging batteries with relatively cheap power)during non-peak time periods or in the third operating mode (e.g.,selling power back to the utility) during peak time periods.

In addition, the third example method 220 may be modified to incorporatethe step 174 of the second example method 150 to allow even moresophisticated control of the first example UPS system 20. Employing boththe step 174 and the step 244 allows the first example UPS system 20 toprevent the UPS system 20 from operating in the third operating mode ifthe battery array 34 is outside of certain predetermined parametersand/or if the profit margin exceeds the cost associated with chargingand discharging the battery.

Referring now to FIG. 5 of the drawing, depicted therein is a secondexample UPS system 320 constructed in accordance with, and embodying,the principles of the present invention. The example UPS system 320 isadapted to obtain power from and supply power to a utility 322 and alsoto provide power to a primary load 324. As depicted in FIG. 5, a meter326 may be connected between the utility 322 and the second example UPSsystem 320. In addition, UPS system such as the first and second exampleUPS system 20 and 320 may be used in connection with a remote monitoringsystem 328 as will be described in further detail below.

Like the first example UPS system 20, the second example UPS system 320is designed to be used to provide power to a larger communicationssystem (partly represented in FIG. 5 by the primary load) based on an ACutility power signal generated by a electrical utility. Examples ofcommunications systems that might use the UPS system 320 are cable TV(CATV) systems, telephony systems, and cellular telephone systems. Andlike the first example UPS system 20, the communications systemcomprises at least a plurality (two or more) and typically many UPSsystems, including a plurality of the second UPS systems 320. Only oneof the third example UPS systems 320 is depicted in FIG. 5 for purposesof clarity.

Typically, the utility 322 operates at a standard voltage (V₁), whilethe primary load 324 operates at a different voltage level (V₂) than theutility 322. The transformer 330 thus steps the voltage up or down asnecessary to perform the functions described below. In addition, theprimary load 324 may operate in some environments (e.g., CATV systems)based on an AC power signal and in other environments (e.g., telephonysystems) based on a DC power signal. As is conventional, the batteryarray 334 is one or more batteries that employ a DC power signal.

The second example UPS system 320 comprises transformer 330, an invertercircuit 332, a battery array 334, a controller 336, and a servicedisconnect 338. The service disconnect 338 may be operated to disconnectthe transformer from the utility 322. The transformer 330 comprises acore 340, a first winding 342, a second winding 344, and a third winding346.

In addition, the third example UPS system 320 comprises a primaryalternative energy source 350 and a charge controller 352. The examplealternative energy source 350 is an array of solar panels, and thecharge controller 352 generates a charge signal appropriate for chargingthe battery array 334 based on the electrical output of the solarpanels. Optionally, one or more secondary alternative energy sources354, such as wind or water turbines, may be provided. The chargecontroller 352 may be configured to generate an appropriate chargesignal additionally based on the electrical output of the secondaryalternative energy source or sources 354, if available.

The third example UPS system 320 may be configured to operate in one ormore of at least three operating modes. In a first (primary) operatingmode, the UPS system 320 supplies power to the primary load 324 andcharges the battery array 334 using power from the utility 322. In asecond (standby) operating mode, the UPS system 320 supplies power tothe primary load 324 using power stored in the battery array 334. In athird operating (peak shaving) mode, the UPS system 320 supplies powerto the utility 322 using power stored in the battery array 334 and/orbattery generated by the primary and/or secondary alternative energysources 350 and 352. In the second example UPS system 320, thecontroller 336 determines whether the UPS system operates in the first,second, or third modes.

As discussed above with reference to the first example UPS 20, the useof the third operating mode allows the operator of the second exampleUPS system to optimize the use of assets (e.g., batteries, solar panels,wind turbines, water turbines) that may be underused or which maygenerate too much capacity for use by the primary load 324 and/orbattery array 334.

In addition, the use of the remote monitoring system 328 allows thecontroller 336 to have up-to-date rate and other information for use indetermining whether the UPS system 320 operates in the first, second, orthird modes.

Referring now to FIG. 6 of the drawing, depicted therein is a fourthexample method 360 that may be implemented by the controller 336 of thesecond example UPS system 320. The fourth example method 360 begins at ainitial step 370 and initially proceeds to a step 372 which determineswhether the utility power signal generated by the utility 22 is withincertain predetermined conditions (i.e., acceptable). If not, the method360 places the UPS system 20 in the second operating mode at step 374and returns to the initial step 370.

If the utility power signal generated by the utility 22 is within thepredetermined conditions, the method 360 moves to step 380, whichdetermines whether the utility 22 is supplying power at peak or non-peakrates. If the utility 22 is supplying power at non-peak rates, themethod 360 places the system 20 in the first operating mode at step 382and then returns to the initial step 370.

If the utility 22 is supplying power at peak rates, the second examplemethod 360 proceeds to a step 384 at which it is determined whether anacceptable alternative energy source is available to the UPS system 320.The acceptable energy source may be one or more of the battery array334, the primary alternative energy source 350, or (if used) thesecondary alternative energy source 354. Factors such as availability ofsunlight and the wear on the battery array 334 or the alternative energysources 350 and 354 may be considered at step 384. The method 360returns to the initial step 370 if the alternative is not available atstep 384.

If the alternative is available at step 384, the method 360 proceeds tostep 386 at which it is determined whether the difference between peakand non-peak rates is sufficient to justify the discharge/charge cycleon the battery array 334 required to sell power back to the utility 22.If step 386 determines that this margin is too low to justify thereduction in battery life, the method 360 returns to the initial step370 and does not place the example UPS system 320 into the thirdoperating mode.

If, on the other hand, the margin is within predetermined parameters(e.g., above a minimum), the method 360 places the system 320 in thethird operating mode at step 390 and then returns to the initial step370.

Referring now to FIG. 7 of the drawing, depicted therein is a thirdexample UPS system 420 constructed in accordance with, and embodying,the principles of the present invention. The example UPS system 420 isadapted to obtain power from and supply power to a utility 422 and alsoto provide power to a primary load 424. As depicted in FIG. 7, a meter426 may be connected between the utility 422 and the third example UPSsystem 420. In addition, the third example UPS system 420 may be used inconnection with a remote monitoring system 428 as will be described infurther detail below.

Like the first example UPS system 20, the third example UPS system 420is designed to be used to provide power to a larger communicationssystem (partly represented in FIG. 7 by the primary load) based on an ACutility power signal generated by a electrical utility. Examples ofcommunications systems that might use the UPS system 420 are cable TV(CATV) systems, telephony systems, and cellular telephone systems. Andlike the first example UPS system 20, the communications systemcomprises at least a plurality (two or more) and typically many UPSsystems, including a plurality of the second UPS systems 420. Only oneof the third example UPS systems 420 is depicted in FIG. 7 for purposesof clarity.

Typically, the utility 422 operates at a standard voltage (V₁), whilethe primary load 424 operates at a different voltage level (V₂) than theutility 422. The transformer 430 thus steps the voltage up or down asnecessary to perform the functions described below. In addition, theprimary load 424 may operate in some environments (e.g., CATV systems)based on an AC power signal and in other environments (e.g., telephonysystems) based on a DC power signal. As is conventional, the batteryarray 434 is one or more batteries that employ a DC power signal.

The third example UPS system 420 comprises transformer 430, an invertercircuit 432, a battery array 434, a controller 436, and a servicedisconnect 438. The service disconnect 438 may be operated to disconnectthe transformer from the utility 422. The transformer 430 comprises acore 440, a first winding 442, a second winding 444, and a third winding446.

In addition, the third example UPS system 420 comprises a primaryalternative energy source 450 and a charge controller 452. The examplealternative energy source 450 is an array of solar panels, and thecharge controller 452 generates a charge signal appropriate for chargingthe battery array 434 based on the electrical output of the solarpanels. Optionally, one or more secondary alternative energy sources454, such as wind or water turbines, may be provided. The chargecontroller 452 may be configured to generate an appropriate chargesignal additionally based on the electrical output of the secondaryalternative energy source or sources 454, if available.

FIG. 7 further illustrates that the example UPS system 420 comprises amotor generator 456 for generating an electrical signal appropriate forcharging the battery array 434 based on a supply of fuel 458.

The third example UPS system 420 may be configured to operate in one ormore of at least three operating modes. In a first (primary) operatingmode, the UPS system 420 supplies power to the primary load 424 andcharges the battery array 434 using power from the utility 422. In asecond (standby) operating mode, the UPS system 420 supplies power tothe primary load 424 using power stored in the battery array 434. In athird operating (peak shaving) mode, the UPS system 420 supplies powerto the utility 422 using power stored in the battery array 434 and/orbattery generated by the primary and/or secondary alternative energysources 450 and 454. In the third example UPS system 420, the controller436 determines whether the UPS system operates in the first, second, orthird modes.

As discussed above with reference to the first example UPS 20, the useof the third operating mode allows the operator of the third example UPSsystem to optimize the use of assets (e.g., batteries, solar panels,wind turbines, water turbines, motor generators) that may be underusedor which may generate too much capacity for use by the primary load 424and/or battery array 434.

In addition, the use of the remote monitoring system 428 allows thecontroller 436 have up-to-date rate and other information for use indetermining whether the UPS system 420 operates in the first, second, orthird modes.

The third example UPS system 420 may be operated using a method similarto the example method 360 discussed above. In particular, If it isdetermined at step 380 that the utility 22 is supplying power at peakrates, the method also considers at step 384 whether the cost of thefuel 458 required to operate the motor generator 456 renders the motorgenerator 456 an acceptable alternative energy source for operating theUPS system 420 in the third mode.

1. An uninterruptible power supply for supply electrical power to aload, comprising: a connection to a primary source for supplying primarypower; a battery system for storing battery power; an inverter; acontroller for controlling the inverter to operate in a first mode inwhich power is supplied to the primary load and the battery system basedon primary power, a second mode in which power is supplied to theprimary load based on battery power, and a third mode in which power issupplied to the primary source based on battery power.
 2. Anuninterruptible power supply as recited in claim 1, in which thecontroller controls the inverter to operate in the first, second, andthird modes based on at least one characteristic of the primary power.3. An uninterruptible power supply as recited in claim 1, in which thecontroller controls the inverter to operate in the first, second, andthird modes based on a cost of the primary power.
 4. An uninterruptiblepower supply as recited in claim 1, in which the controller controls theinverter to operate in the first, second, and third modes based on adifferential between the cost of the primary power and a cost associatedwith operation of the battery system.
 5. An uninterruptible power supplyas recited in claim 1, in which the controller controls the inverter tooperate in the first, second, and third modes based on a voltage of theprimary power.
 6. An uninterruptible power supply as recited in claim 1,in which the controller controls the inverter to operate in the first,second, and third modes based on a presence of the primary power.
 7. Anuninterruptible power supply as recited in claim 1, in which thecontroller controls the inverter to operate in the first, second, andthird modes based on at least one of a cost of the primary power, avoltage of the primary power, and a presence of the primary power.
 8. Anuninterruptible power supply as recited in claim 1, in which thecontroller controls the inverter to operate in the first, second, andthird modes based on at least one characteristic of the battery system.9. An uninterruptible power supply as recited in claim 1, in which theprimary source is a utility.
 10. An uninterruptible power supply asrecited in claim 1, further comprising at least one secondary source forproviding secondary power, wherein: in the first mode, power is furthersupplied to the primary load and the battery system based on secondarypower; in the second mode, power is supplied to the primary load basedon secondary power; and in the third mode, power is supplied to theprimary source further based on secondary power.
 11. An uninterruptiblepower supply as recited in claim 1, further comprising at least onegenerator for providing generator power, wherein: in the first mode,power is further supplied to the primary load and the battery systembased on generator power; in the second mode, power is supplied to theprimary load based on generator power; and in the third mode, power issupplied to the primary source further based on generator power.
 12. Amethod of supplying electrical power to a load, comprising the steps of:providing a battery system for storing battery power; providing aninverter; controlling the inverter to operate in a first mode in whichpower is supplied to the primary load and the battery system based onprimary power obtained from a primary power source, a second mode inwhich power is supplied to the primary load based on battery power, anda third mode in which power is supplied to the primary source based onbattery power.
 13. A method as recited in claim 1, in which inverter iscontrolled to operate in the first, second, and third modes based on atleast one characteristic of the primary power.
 14. A method as recitedin claim 1, in which the inverter is controlled to operate in the first,second, and third modes based on at least one characteristic of thebattery system.
 15. An uninterruptible power supply for supplyelectrical power to a load, comprising: a connection to a primary sourcefor supplying primary power; a battery system for storing battery power;an inverter; a transformer operatively connected between the primarysource, the battery system, and the load; and a controller forcontrolling, based on at least one characteristic of the primary power,the inverter to operate in a first mode in which power is supplied tothe primary load and the battery system based on primary power, a secondmode in which power is supplied to the primary load based on batterypower, and a third mode in which power is supplied to the primary sourcebased on battery power.
 16. An uninterruptible power supply as recitedin claim 1, in which the controller controls the inverter to operate inthe first, second, and third modes based on at least one of a cost ofthe primary power, a voltage of the primary power, and a presence of theprimary power.
 17. An uninterruptible power supply as recited in claim16, in which the controller controls the inverter to operate in thefirst, second, and third modes based on at least one characteristic ofthe battery system.
 18. An uninterruptible power supply as recited inclaim 1, in which the primary source is a utility.
 19. Anuninterruptible power supply as recited in claim 18, further comprisingat least one secondary source for providing secondary power, wherein: inthe first mode, power is further supplied to the primary load and thebattery system based on secondary power; in the second mode, power issupplied to the primary load based on secondary power; and in the thirdmode, power is supplied to the primary source further based on secondarypower.
 20. An uninterruptible power supply as recited in claim 19,further comprising at least one generator for providing generator power,wherein: in the first mode, power is further supplied to the primaryload and the battery system based on generator power; in the secondmode, power is supplied to the primary load based on generator power;and in the third mode, power is supplied to the primary source furtherbased on generator power.